The invention relates to shoe machinery in general, and more particularly to improvements in apparatus for treating the lasting edges of shoe uppers. Still more particularly, the invention relates to improvements in apparatus for so-called pulling of lasting edges of lasted shoe uppers over insoles.
German Pat. No. 28 45 303 discloses an apparatus wherein the lasting edge of a lasted shoe upper is pulled over the insole by a pair of rigid frustoconical shafts having oppositely inclined integral screw threads. The shafts are driven to rotate in opposite directions whereby the screw threads pull the lasting edge over the insole which overlies the underside of the last for the shoe upper. The shafts are parallel to each other and are journalled in a bearing sleeve which is pivotable about an axis that is adjacent the median portions of the shafts and extends transversely of the shafts. The pivotability of the bearing sleeve is considered necessary in order to enable the shafts to be oriented in a manner such as to maintain their threads in engagement with the lasting edge, i.e., to conform their inclination to the inclination of the adjacent portion of the last.
A drawback of the patented apparatus and of other apparatus which for many decades employ rigid shafts with rigidly affixed or integral threads is that portions of the lasting edge are likely to be subjected to excessive stresses because the threads of the shaft or shafts do not bear against the lasting edge with a uniform force, either because the insole is curved or because the mounting and design of the shaft or shafts and their threads do not allow for accurate conformance of the threads to the lasting edge which overlies the insole.